This invention relates generally to control systems that employ distributed data (intelligence) processing, and more particularly to wind turbine control systems wherein multiple microprocessors are employed instead of a central processor.
Historically, microprocessor based wind turbine control systems have been designed, developed and manufactured using a single central processing unit which handles all input, output, calculation, logic, and data manipulation functions. Such centralized processing requires multiplexed input/output functions and relatively large interrupt driven programs to handle the complexity of wind turbine control. This design approach has certain objectionable aspects due to the following reasons:
1. The processors' inability to monitor and control each input/output port simultaneously. Although some real time data can be processed, the large input/output requirements mean that most functions will be allocated on a shared priority basis.
2. Because of the turbine controller's large requirements for input/output data, peripheral integrated circuits are required to expand the functional ability of the processor. These peripheral circuits increase the complexity of the central processing unit design, decreasing its long term reliability and increasing its maintenance cost.
3. Such complex centralized designs also require relatively large programs, which are much more difficult and time consuming to analyze, test and debug. Software development time can easily outstrip hardware development time in such large programs, and therefore project management can be complicated due to problems associated with judging the time required for such programming.
4. Traditionally, the manufacturing method for such centralized design has been to locate all of the electronic components on a single printed circuit board making maintenance cumbersome, time consuming, and relatively expensive.
A typical centralized processor employs an address and data bus to expand the functional ability of the processor through such external integrated circuits, such as a Peripheral Interface Adapter (PIA), External Random Access Memory, special timing circuits, serial port adapters, and Analog to Digital Conversion. In addition, most processor based control systems used in wind turbine controller environments require external Read Only Memory for the program residence. In a typical wind turbine application, the program residence can occupy as many as three or four ROM chips. External Random Access Memory for data storage and manipulation can also occupy several chips, and it is not uncommon to see two or three PIA chips in order for the processor to deal with the large input/output requirements of the control system. Other external peripheral integrated circuits can include special timer chips, and serial port adapters. As the number of these chips grows, so does the control bus logic, thereby increasing the complexity of the design.